1. Field of the Invention
The present invention relates to an ion implantation apparatus and method.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, ion implantation carried out to introduce impurities into the semiconductor substrate is affected by a phenomenon called channeling. Channeling is a phenomenon in which, when the direction in which an ion beam impinges at the semiconductor substrate coincides with the crystal orientation of the semiconductor substrate, many impurities reach deeper than the position of a peak value of the impurity profile obtained when the ion implantation direction does not coincide with the crystal orientation. The magnitude of channeling depends on the angle at which ions are implanted into the semiconductor substrate (perpendicularity); therefore, the characteristics of a semiconductor device formed on the semiconductor substrate vary according to the perpendicularity. Accordingly, control of the perpendicularity is important.
At present, however, the accuracy of the angle between the trajectory of the ion beam and the processed surface of the semiconductor substrate, which is involved in the determination of perpendicularity, depends on the mechanical precision of the ion implantation apparatus. In other words, the ion implantation apparatus is not configured so as to observe the relative relationship between the trajectory of the ion beam and the processed surface of the semiconductor substrate and control the perpendicularity accordingly. That is, in general, a plumb and a level are used to find a perpendicular and a parallel plane relative to the direction of gravity for use as reference lines and an ion implantation apparatus is assembled with reference to these reference lines. For this reason, the reference lines vary according to the accuracy to which parts of the ion implantation apparatus are processed and the accuracy to which these parts are assembled. As the result, the perpendicularity varies from apparatus to apparatus.
Some ion implantation apparatus have function to measure the trajectory of the ion beam and adjust it. The apparatus, however, measures only the trajectory to a measuring instrument and does not measure the angle between the measuring instrument and the substrate. As a result, it cannot detect the change of the angle between the measuring instrument and the substrate. This leads failure to detect possible change of the angle between the trajectory of the ion beam and the substrate.
As described above, at present, the relative relationship between the trajectory of an actual ion beam and the processed surface of a semiconductor substrate is not observed. For this reason, even if, its condition changes due to some factors and consequently the perpendicularity changes after an ion implantation apparatus has been assembled, it is impossible to notice and correct this situation. From the same reason, it is impossible to detect variations in perpendicularity from substrate to substrate, which can produce variations in device performance.